The Patagonian steppeecoregion extends approximately from the mid-Andean Precordillera southward, terminating immediately north of the Strait of Magellan near the Rio Gallegos. This steppe is bounded on the west by the cold temperate forest slopes of the Andes Range, and on the east by the Atlantic Ocean. It extends northwest as shrubland steppe and to the north as thorn thicket, gradually making the transition to Argentine Monte. This area is a cold desert scrub steppe, with very high wind velocities throughout the year, as well as year around frosts likely. This ecoregion has high levels of endemism for both plants and animals.

Location and general description

The Patagonian steppe ecoregion mainly covers the Patagonia region of Argentina from the Atlantic Ocean shore across the border and into easten Chile. The Peninsula Valdés is an outlier of this ecoregion, lying slightly north of the main body. The topography of this ecoregion includes low-lying mountains, plateaus and plains. Soils are variable but generally exhibit a rocky-sandy composition that are deficient in fine-grained materials and organic matter. The climate is very arid and cold with snow during the winter and nighttime frosts practically year-around; however, annual precipitation does not typically reach more than 200 millimetres (mm). A characteristic of the Patagonian climate is a persistent desiccating wind that arrives with great force from the west, particularly in the summer months. Austral winter generally lasts for five months from about June to September, with averages of the coldest month between one to three °Celsius below freezing. Elevations range considerably in this expansive ecoregion from sea level nearer the shores of the Atlantic up to 2000 metres (m) in the north and about 700 m in the southern extent of the ecoregion, due to the Andean slopes on the western side.

Santa Cruz, Argentina. Source: WWF/Patricia & Steve Bremer

In general, the vegetation of this steppe ecoregion is xerophytic and highly adapted for protection against drought, wind, and herbivores. The vegetation is considered strongly related to Andean flora however the average numbers of endemic species for dominant families is very high with as much as 60 percent endemism in Leguminosae and 33 percent in Compositae families. Three main types of vegetative communities are exhibited in the Patagonian steppe. The most common type is semi-desert (45%), with shrub-steppe (30%) in second place, and grass-steppe (20%) in third place in terms of percent of occurrence. Desert-like areas also exist here with little to no vegetative cover; however, some wet meadow areas are present which have close to 100% plant cover.

Semi-desert vegetation has highly adapted features; these dwarf and cushion shrubs are the most widely occuring vegetation type in the ecoregion. Shrubs species of Acantholippia, Benthamiella, Nassauvia and Verbena genera grow in these areas as well as cushion plants of Mulinum spinosum and Brachyclados caespitosus and tuft grasses; the most common being species of Poa and Stipa. Also abundant are species with heteroblastic growth and small limited-growth branches covered with tight leaves. Junellia tridens and Nassauvia glomerulosa are good examples of this type of plant. Taller woody shrubs indicate a change to shrub steppe communities within the ecoregion. These species of Anarthrophyllum, Berberis, Schinus, and Verbena can grow up to three meters in height. Valleys and lowlands with higher amounts of water available to vegetation host species of sedges (Eleocharis), rushes (Juncus), grasses (Agrostis, Hordeum, Polypogon), and in saline areas certain halphytic species (Distichlis, Nitrophila, Puccinellina).

Biodiversity

In this ecoregion one finds two endemic species of the Mesquite genus Prosopis, one species of Creosote Bush, Larrea, and some species within the genera Wolfberry (Lycium) and Peppertree (Schinus). Genera and species endemism are extremely high in the Patagonian steppe, notably among the plant genera Philippiella, Neobaclea, Xerodraba, Benthamiella, Pantacantha, Duseniella, Eriachaenium and Lepidophyllum. There are also numerous endemic species of mammals, birds, and amphibians. The National Council for Bird Preservation asserts that this ecoregion is one of the most important in terms of the presence of endemic bird species, and posits that there are likely ten such avian species here. The fauna is quite varied in the Patagonian steppe. There have been a total of 363 native vertebrates recorded within the Patagonian steppe ecoregion.

Marine margins

The Argentine coasts have high speciesdiversity, including 33 species of cetaceans, eight species of pinnipeds and more than 450 fish species in the waters of the Argentine Sea.

Current status

Despite the low density of the human population, this ecoregion has been significantly adversely affected due to the fragility of the environment, especially due to overgrazing of introduced livestock over large portions of the Patagonian steppe. This ecoregion has numerous natural reserves and protected areas. These include the Laguna Blanca National Park (Ramsar), Nahuel Huapi National Park, Perito Moreno National Park, Los Glaciares National Park, Bosques Petrificados Natural Monument, El Payén Provincial Reserve, El Tromen Provincial Reserve, Domuyo Provincial Reserve, Somuncurá Provincial Reserve, Laguna Aleusco Provincial Reserve, Bosques Petrificados José Ormachea Provincial Reserve, Bahía San Julián Provincial Reserve, and Península de Valdés Provincial.

Types and severity of threats

The major problem is desertification due to overgrazing primarily by domesticated sheep, damaging the limited plant coverage and exposing the soil to erosion. In addition to the topsoil loss, native fauna are being displaced by enormous numbers of domesticated livestock, who are competing for the same biomass of grass stocks. Many species of fauna are also now in regression due to the tempting prices paid for the skins of chulengos (baby guanacos) and choique rhea feathers. There is also pressure on foxes and pumas from hunting and/or poisoning because they are persecuted for being considered by some ranchers as a potential threat to flocks.

Justification of ecoregion delineation

Within Argentina the delineations for the Patagonian Steppe were derived from Daniele and Natenzon, and linework follows their "Estepa Arbustiva Patagónica Arida (arid Patagonian woodland steppe)" region. Other resources consulted include Cabrera and Morello. The linework for the western portion and within Chile was modified according to UNESCO and expert opinion at ecoregional priority setting workshops: Valdivia, Chile, Bariloche, Argentina, and Concepción, Chile.

Disclaimer: This article contains some information that was originally published by the World Wildlife Fund. Topic editors and authors for the Encyclopedia of Earth have edited its content and added new information. The use of information from the World Wildlife Fund should not be construed as support for or endorsement by that organization for any new information added by EoE personnel, or for any editing of the original content.